Some parts of District 6 sink by 5 centimeters a year, the survey revealed.

Experts who carried out the survey pointed to the over-exploitation of groundwater as the leading cause of the problem.

Around 670,000 cubic meters of underground water are extracted per day by both residents and companies in HCMC, which is home to more than eight million people and considered the country's economic hub.

Along with the fast pace of urbanization, the over-extraction of groundwater has caused aquifers to shrink, leading to sinkage, according to the survey.

The survey's authors urged the city government to come up with measures to significantly reduce the volume of groundwater extraction.

Earlier this year, officials from the Ministry of Natural Resources and Environment proposed a groundwater pumping ban on a 195-square-kilometer area that spans districts 1-7,10, 11 and Nha Be, citing lower groundwater levels and higher risk of sinkage than other parts of the city.

The city administration plans to reduce groundwater exploitation to 440,000 cubic meters a day by 2015 and 100,000 cubic meters a day by 2025 by increasing the use of treated water drawn from the Dong Nai and Saigon rivers.